As a countermeasure against soilborne pathogen and a measure to increase a yield, grafting has been increasingly used worldwide. A tube or an elastic cylindrical body (see Patent Documents 1 and 2 or the like), a clip (see Patent Document 3 or the like), an adhesive tape (see Patent Documents 4 through 6 or the like), heat-shrinkable plastic (see Patent Document 7 or the like), and stretch non-woven cloth (see Patent Document 8 or the like) have been conventionally used as a joint material for joining a rootstock and a scion in grafting.